I have some ideas that sound interesting and want to know how difficult they could be to implement.

1. new instruments (organ, choir, orchestra, band)
2. tuning
3. sound effects like clicks, beeps, and everyday noises
4. fix the glitch that when dragging a X amount of stanzas notes seem to vanish then zoom off far away
5. add glissando (rapid sliding with hand over notes)
6. add more music theory (pedal, staccato, forte, piano, etc.)
7. Remove censor as an option
8. time signatures
9. title in chat next to mods and admins so you dont piss them off by accident
10. make it easier to add friends on the sequencer
11. tempo changes in song
12. smart editor (click and hold a note to have a tab appear that shows what you can do whole, half, dotted, quarter, etc) for beginners
13. add the ability to move chat to sidebar on the forum
14. weird glitch that importing midis with 32nd notes the 32nd notes dont appear
15. big songs dont load correctly i.e greater then 60k notes
16. add a sub note in chat to show who is typing (like discord)

Here are my plausibility ratings:
(disclaimer - I'm not the owner, so these may not be accurate)
1. new instruments (organ, choir, orchestra, band)
Soon, although this just happened in recent history.
2. tuning
Possible with 8-bit easily, but idk about other instruments.
3. sound effects like clicks, beeps, and everyday noises
Easy peasy, can fit in existing percussion.
4. fix the glitch that when dragging a X amount of stanzas notes seem to vanish then zoom off far away
If only it was easier done than said. Idk if we know why that even happens, and if so, how to fix it.
5. add glissando (rapid sliding with hand over notes)
Already in the sequencer, just get creative.
6. add more music theory (pedal, staccato, forte, piano, etc.)
Pedal is already kind of in with reverb, staccato should be possible but it would change the sound of existing sequences (maybe a version flag?), forte/piano is already kind of in with note stacking and volume adjustment though it is really bodgy.
7. Remove censor as an option
Type [i][/i] in between anything you want to be uncensored, i.e. "di[i][/i]e". Would be a nice option though, probably easy-ish.
8. time signatures
Already in. Go to your browser console (look it up if you don't know what it is) and type "grid=3/4" (without the quotes) to make the time signature 3/4, for example.
9. title in chat next to mods and admins so you dont piss them off by accident
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pls (already in forums but not chat iirc)
10. make it easier to add friends on the sequencer
That's a myBB thing I believe, though it could be done probably. Maybe have joint ownership of sequences as a feature? Actually that would be cool.
11. tempo changes in song
It could be done by making the tempo a automation track, although the UI would be a pain probably. Automation UI would probably be the overall next step for OS in terms of automation.
12. smart editor (click and hold a note to have a tab appear that shows what you can do whole, half, dotted, quarter, etc) for beginners
nah, too useless
13. add the ability to move chat to sidebar on the forum
idk why this isn't fixed
14. weird glitch that importing midis with 32nd notes the 32nd notes dont appear
Try fast graphics?
15. big songs dont load correctly i.e greater then 60k notes
They do, just wait.
16. add a sub note in chat to show who is typing (like discord)
Too hard/laggy probably.